1. Field of the Invention
Embodiments of the present invention relate generally to cathodic protection of structures in corrosive environments. In particular, embodiments of the invention relate to systems and methods for monitoring the condition of galvanic anodes disposed internally within a fluid-containing vessel for the cathodic protection of the fluid-containing vessel.
2. Description of the Related Art
Cathodic protection systems are often employed for the protection of metallic structures from corrosion. The protected metallic structures are arranged to serve as a cathode in an electrical circuit such that oxidation of the metallic structures are restricted. A sacrificial anode is often supplied to the circuit to support a net oxidation reaction.
One type of metallic structure that is often protected by a cathodic protection system is a fluid-containing vessel such as a storage tank, cylinder, settling tank or process equipment for processing fluids associated with the production of energy. These fluid-containing vessels generally include an interior chamber in which a corrosive fluid is stored and isolated from an exterior environment. A galvanic anode, such as a magnesium, aluminum or zinc anode, is often disposed within the interior chamber to protect structural steel portions of the fluid-containing vessel. Magnesium anodes often demonstrate high potential and, thus, corrode in less than one year in vessel protection applications. Aluminum anodes are also consumed rapidly, particularly when the temperature is more than 50° C. in the vessel. Typical zinc anodes are not consumed as quickly, but tend to reverse polarity at higher temperatures. Thus, typical zinc anodes can cease serving as protective anodes, and become the cathode in the electrical circuit at high temperature. High-temperature zinc (“HTZ”) anodes are often used in vessels at temperatures above 50° C. and up to 70° C., and exhibit a longer service life than typical zinc anodes.
Frequent monitoring of the condition of galvanic anodes is required to verify wear levels of the galvanic anodes and proper operation of the cathodic protection system. Direct observation of the galvanic anodes is often not feasible due to their location within the interior chamber of the fluid-containing vessel. Current and voltage measurements associated with the cathodic protection system enable an operator to assess the wear conditions of these galvanic anodes, but taking these measurements can be a dangerous, time-consuming and labor-intensive process.